The Collaborative International Dictionary of English v.0.48:

Semiconscious \Sem`i*con"scious\, a.
   Half conscious; imperfectly conscious. --De Quincey.
   [1913 Webster]

WordNet (r) 3.0 (2006):

semiconscious
    adj 1: partially conscious; not completely aware of sensations

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "semiconscious":
   asleep, cataleptic, catatonic, cold, comatose, dead, doped,
   drugged, half-conscious, narcotized, nirvanic, oblivious, out,
   out cold, out of it, senseless, spaced out, stoned, strung out,
   unconscious, zonked, zonked out